Device-to-Device (D2D) technology is receiving a lot of attention because of the ability to offer new services, improve system throughput, and offer a better user experience. A variety of potential use cases for D2D have been identified.
In order to ensure successful D2D communications, synchronization is crucial: D2D transmitting and receiving user equipments (UEs) should acquire the same time and/or frequency synchronization from synchronization source(s). These sources need to periodically transmit at least a D2D synchronization signal (D2DSS) to ensure D2D UEs derive time and/or frequency synchronization. The synchronization source could be a base station, an evolved NodeB (eNodeB) (like a traditional Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) network), or a D2D UE which is relaying the downlink (DL) synchronization channel from an eNodeB.